A hybrid-electric or all-electric vehicle has a traction battery to store and provide energy for vehicle propulsion. In order to improve performance and battery life, it is necessary to operate the battery within certain limits. Operating the battery outside of the limits may decrease the performance or life of the battery. An important quantity for controlling and operating the battery pack is the battery power capability. The battery power capability indicates how much power the battery is capable of providing (discharge) or receiving (charge) in order to meet driver and vehicle demands.
A battery pack may be modeled by an equivalent circuit model (ECM) having an arrangement of impedance components. The ECM may depend on the type and chemistry of the battery being used. The battery power capability may be calculated based on the battery impedance component values of the model. The battery impedance component values may vary with age and temperature of the battery.
A recursive parameter estimation method, such as an Extended Kalman Filter (EKF) may be used to identify battery equivalent circuit model impedance parameters. A shortcoming of the EKF is that it may require some time to converge to the true parameter values. The convergence time may be a function of the starting values that are used to initialize the EKF. The convergence of the EKF may be influenced by an efficient choice of the initial parameter values. A poor choice of initial EKF parameters may lead to divergence of the parameter identification process in which case a reasonable estimate of the true battery impedance parameter values may never be obtained. In addition, prior to convergence of the EKF, the battery impedance parameter estimates from the model may not provide acceptable results for calculating the battery power capability.